All standard water heaters have a TPR valve, but many are missing a discharge pipe. “TPR” stands for temperature and pressure relief. Temperature and pressure go hand-in-hand; as temperature increases, so does pressure. Believe it or not, a water heater can build up enough pressure to shoot several stories out a roof like a rocket and cause immense damage. Fortunately, they are equipped with a TPR valve to prevent that from happening.
TPR valves are designed to open when the temperature and pressure inside the tank reach an unsafe level. Rather than the pressure building up inside the tank and causing an explosion because it has nowhere to go, the water/steam will exit through the TPR valve.
Now, the TPR valve itself is not the common defect that we inspectors often see. All standard water heaters are built with the valve attached, so the valve is never missing. What IS often missing (about half the time or more in my experience) is a discharge pipe that is required to be attached to the valve. The pipe should run straight downward and end several inches from the floor, leaving a small “air gap” between the floor and the pipe. If a floor drain is present, discharge pipes are often routed to the drain so the water exits the space rather than pooling up on the floor.
The reason these discharge / extension pipes are required is that if anyone happened to be near the water heater when the discharge pipe opened, they could possibly be scorched by the water leaving the valve. With the pipe attached, the water will instead flow through the pipe toward the ground and the potential for injury is greatly reduced.
TPR valves also exist on boilers for the same reason; but while only some homes have boilers, all homes have water heaters, and most homes still have tank water heaters, not tankless.
Check your water heater to make sure it has a discharge pipe properly attached to the TPR valve and running downward toward the floor. The TPR valve will likely be brass and either on the top of the water heater or on the side close to the top. If the pipe is missing, contact a qualified plumber immediately to get the pipe installed. The small cost to have this simple repair done far outweighs the potential risk.
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